For more technical explainers on PowerShell, read our updated 2021 report: PowerShell 101: A Technical Explainer for IT Pros.
Q: I'm trying to invoke commands on a remote server in PowerShell, but any variables I try to use are failing. What can I do?
A: PowerShell variables are great for storing information that's available within the PowerShell session. For example:
$message = "Message to John" write-host $message
would output the text contained in the $message variable with no problem. Now consider running the same command on a remote machine:
$message = "Message to John"
Invoke-Command -ComputerName savdalhv20 -ScriptBlock {write-host $message}
Nothing shows in the output. The reason for this is that Invoke-Command creates a new PowerShell session on the remote machine that doesn't have the variables you defined locally available and therefore contains no data.
If you want to use variables in a remote session, such as with Invoke-Command, you need to pass those variables as parameters to the script block that will be used with Invoke-Command and then the actual value as an argument. For example:
$message = "Message to John"
$ScriptBlockContent = {
param ($MessageToWrite)
Write-Host $MessageToWrite }
Invoke-Command -ComputerName savdalhv20 -ScriptBlock $ScriptBlockContent -ArgumentList $message
This now works; the text in the message is output to the screen. This is because the code being run remotely via Invoke-Command is writing a variable, $MessageToWrite, which is expected as a parameter when used and is populated with the value of $message via the -ArgumentList. Therefore, when you want to use variables that are defined locally, you must pass them as parameters to the remote session.
